Incidentally, this reminds me: there ought to be a specific term for the glee experienced when one's post or comment is voted into the karma stratosphere.
I suggest "Yvainity."
(Sorry, I couldn't resist. No offense to Yvain, whose posts deserve their high ratings!)
A fun game you can play on LessWrong is to stop just as you are about to click "comment" and make a prediction for how much karma your comment will receive within the next week. This will provide some quick feedback about how well your karma predictors are working. This exercise will let you know if something is broken. A simpler version is to pick from these three distinct outcomes: Positive karma, 0 karma, negative karma.
What other predictors are this easy to test? Likely candidates match one or more of the following criteria: